1. Field of the Invention
This invention relates to switchgear assemblies for electric power distribution systems. More particularly, it relates to the construction and support of the rigid electrical conductors forming buses which route the power within the switchgear cabinet, and especially to the conductors which form the stabs engaged by the quick disconnect electrical connectors on the electrical apparatus housed within the switchgear cabinet.
2. Background Information
Switchgear assemblies are combinations of electrical apparatus for electric power distribution systems mounted in metal cabinets. The electrical apparatus typically includes switching devices such as circuit breakers and network protectors which provide protection as well as switching, disconnect switches which isolate or separate parts of the distribution system, and transfer switches which are used to connect the system to alternative power sources. A switchgear assembly can also include instrumentation such as metering equipment.
Typically, several pieces of electrical apparatus are mounted in a single cabinet, usually stacked vertically. Multi-phase input and output electrical conductors must be connected to each piece of electrical apparatus. In a common arrangement, a set of multi-phase rigid conductors or bus bars extends transversely through the cabinet. A set of multiphase risers extending vertically within the cabinet behind the electrical apparatus connects the transversely extending conductors with the individual electrical apparatus through stabs which are engaged by quick disconnects on back faces of the electrical apparatus as the apparatus is fully inserted into the cabinet. Another set of rigid conductors, called runbacks, engage other quick disconnects on the electrical apparatus and extend rearward between the risers for connection to cabling extending out of the cabinet.
It is common practice for the conductors interfacing with the electrical apparatus, i.e., the stabs connected to the risers, and the runbacks connected to the cabling, to each be a single, thick, flat copper conductor. Such thick, single piece conductors generally have sufficient stiffness to withstand the very large magnetic forces generated by short circuits to which the equipment may be exposed. Also, at the present rated currents for the electrical apparatus used in such switchgear assemblies, it is not difficult to maintain the electrical spacing required between the conductors.
However, as the current ratings of the electrical apparatus used in switchgear assemblies increases, the increased thickness required of the conductors to accommodate temperature rise restrictions requires machining and drilling of the conductors to produce the necessary configurations and mounting holes in these conductors. The need for such operations increases the cost and time required to manufacture the switchgear assemblies.
In some switchgear, the stabs are formed by bending a flat conductor back on itself with the two sections straddling the associated riser. This produces a rather large radius bend which must be engaged by the quick disconnect. Some quick disconnects cannot accommodate this large radius and instead require a square cut stab end.
Another consideration in switchgear construction is that supports need to be provided for the interface conductors adjacent the quick disconnects. In a common arrangement, the interface conductors are inserted through snug openings in a molded support from the riser side. Hence, the inserted ends of these interface conductors cannot have lateral protrusions.
There is room, therefore, for improvement in the conductors used in switchgear assemblies and in the switchgear incorporating such conductors.